1. Field of the Invention
This invention relates to the treatment of sleep-related breathing disorders such as snoring and obstructive sleep apnea.
2. Related Art
Snoring is a condition that affects people of all ages, but is more common in men once they reach middle-age and in overweight women (Schmidt-Nowara et al., 1995). It is frequently associated with the more serious, and sometimes life-threatening, obstructive sleep apnea (OSA). OSA is a condition where breathing is temporarily interrupted during sleep by obstruction of the airway resulting in episodes of hypoxia. Less serious effects of OSA include sleepiness and lethargy, but if left untreated, it can lead to more serious respiratory and cardiovascular complications (Guilleminault et al., 1976). Although not all snorers suffer from OSA, excessively loud snoring is one of the symptoms of the condition. A second form of sleep apnea, central sleep apnea (CSA) is distinguished from OSA because its underlying cause is neurological and not physical.
Snoring poses not only an inconvenience with regard to the disruption of the sleep-cycle of the sufferer's partner, but can also lead to sleep-deprivation in the sufferer due to repeated arousals from upper respiratory tract resistance even in non-apneic individuals in a condition known as upper airway resistance syndrome (Guilleminault et al., 1991). Such sleep-cycle disruption leads to daytime lethargy and drowsiness and results in a substantial decrease in the quality of life of the sufferer.
Both snoring and OSA are conditions of complex and incompletely understood etiology, but both are the result of obstructed flow due to abnormalities in the geometry of the air passages. In the case of snoring, this abnormal flow results in the vibration of soft tissues in the throat (primarily the soft palate) leading to the generation of sound. In the case of OSA, airflow is so restricted that it ceases intermittently. Some of the morphological features that can contribute to both conditions include; an enlarged tongue volume, a receding jaw that alters the geometry of the pharynx, an enlarged uvula, a lack of muscle tone in the throat leading to a more collapsible pharynx. Repeated trauma to the upper airway tissues due to snoring can damage muscle fibers and peripheral nerve fibers which further impairs muscle stabilization and increases the tendency for obstruction.
Treatments for both snoring and OSA have fallen into two broad classes (Sanders, 1990), namely, surgery and the use of various oral appliances. Surgery aims to modify the geometry of various parts of the respiratory tract, thereby facilitating the smoother passage of air. Procedures include reconstruction of the facial skeleton, tracheostomy, and surgery of the soft palate and/or the pharynx (e.g. uvulopalatopharyngoplasty). Oral appliances are worn during sleep and generally divided into two classes (Lowe, 1994). Mandibular advancing devices are custom-molded to fit the dental profile of the patient and designed to alter the geometry of the throat by pushing forward the lower jaw, thereby widening the air passage. Tongue retaining devices are designed to maintain the tongue in an anterior position to minimize its effect in restricting air flow. In the case of OSA, a third class of device has been developed to provide continuous positive air pressure (CPAP) to the patient. By increasing the pressure of the air breathed in by the patient, CPAP devices help to counter the narrowing of the air passage that leads to OSA.
All of the devices described above can be either inconvenient or uncomfortable to use, and while they all provide some level of efficacy (Schmidt-Nowara et al., 1995), patient compliance can be an issue. In addition, the surgical procedures outlined above range from being moderately to highly invasive and inconvenient.
More recently, three less invasive surgical procedures have been or are being developed for the treatment of snoring.
1. Radiofrequency ablation depends on the use of electromagnetic radiation to heat regions of the soft palate to a temperature of 77-85° C., resulting in vaporization of tissue plus shrinkage of at least some of the remaining tissue and relief of airway obstruction (Fischer et al., 2000). In addition, the damage caused by heating results in the formation of scar tissue that stiffens the palate and reduces its propensity to vibrate in response to the passage of air. This technique has also been reported to have some efficacy in cases of mild to moderate OSA (Blumen et al., 2002). It would be expected, due to the heat denaturation of the remaining target tissue, that the remaining tissue will have inferior mechanical properties, inferior molecular and micro-structural geometry, and eventual loss of some initial treatment-related benefits.
2. Injection of sclerosants such as sodium tetradecyl sulfate into the soft palate results in fibrosis and the formation of scar tissue in a procedure known as Snoreplasty (Brietzke and Mair, 2004; Brietzke and Mair, 2003; Brietzke and Mair, 2001). As in RF ablation, this scar tissue stiffens the palate and helps to prevent vibration. But also, as in RF ablation, this procedure would be associated with a decline in mechanical properties as well as molecular and microstructural structural integrity leading to an eventual loss of some initial treatment-related benefits.
3. The Pillar procedure seeks to relieve snoring by stiffening via the implantation of small fibrous strips into the soft palate using a relatively simple in-patient procedure (Catalano et al., 2007; Romanow and Catalano, 2006; Friedman et al., 2006). The strips themselves serve to physically stiffen the soft palate, but also induce subsequent scar formation that further enhances the stiffening of the tissue. To the extent that this procedure induces scar stiffening, it would be associated with contributing to the decline in mechanical properties of arguably overloaded and already degraded tissues leading to an eventual loss of some initial treatment-related benefits. In addition one would expect that the tissue-material interface could potentially be the site for micro-motion, wear, particle-release, inflammatory or cellular response, and/or tissue damage.
The underlying principal of these three procedures is the stiffening of the soft palate to increase its damping ratio and thereby ameliorate its vibration as air passes over it. While this approach may be generally effective in ameliorating or eliminating snoring, albeit with the numerous long-term concerns noted above, its success in treating OSA is more varied due to the accompanying long-term tissue degradation and the more diverse nature of the etiology of OSA. Nevertheless, some of these treatments have been demonstrated to exhibit some efficacy in some OSA patients (Blumen et al., 2002; Friedman et al., 2006).